where \(\delta _R = 0\)  in the FDH scheme [1]} and \(\delta _R =1\)  in either
conventional dimensional regularization [2]} or the 't
Hooft-Veltman scheme [3]}. One may then propagate
this correction to the gravitational amplitudes through the double
copy.
While the correction is of \(\mathcal {O} (\epsilon )\) , it can interfere with
infrared or ultraviolet singularities to give nontrivial
contributions. However, for the massive amplitudes that we are
computing here, the distinction between different schemes is not
important because the four-graviton amplitudes with massive
matter in the loop are both ultraviolet and infrared finite (see
Sects. REF  and REF ).
